Mr Mitchell told Thein Sein, the general turned president, Britain was ready to "open the door to a whole new world," dropping sanctions and increasing aid, if two key concessions are forthcoming – the release of prisoners and the acceptance of Aung San Suu Kyi into elections as part of the drive to democracy.

A British volte-face on Burma would be certain to unlock a raft of European sanctions on mining, gems and targeted travelling bans on leading families as well as unleash hundreds of millions of pounds for the country.

The Conservative minister pleaded the case of Min Ko Niang, a leader of the 1988 student democracy movement, who he knows from a previous trip as opposition spokesman in 2007. Burma's opposition, backed by Mr Mitchell, is demanding the release of 591 political prisoners.

Mr Min who has campaigned for democracy since leading the successful democracy movement 23 years ago, has been held 600 miles from his family in a prison in Burma's far north. He was arrested for leading protests against fuel price rises in 2007.

"He is a man of magnificent qualities and he is an important part of Burma's future political development," Mr Mitchell said.

Mr Mitchell visited the regime's isolated, grandiose capital for talks with seven senior cabinet ministers, including the vice-president and speaker of parliament. Apart from a brief trip focused on Cyclone Nargis in 2008 no cabinet minister has visited Burma in decades.

The triumvirate who head Burma's civilian government installed after flawed elections last year said a prisoner release was postponed on Monday but would go ahead.

Mr Mitchell said they had assured him that Aung San Suu Kyi, the opposition leader, was a "national" figure with a role in Burma's political future.

Thura U Shwe Mann, the parliament speaker and Burma's second most important figure, told Mr Mitchell that the regime was not, as critics allege, toying with democratic hopes.

"It is irreversible," he said.

The message of reform from the purpose-built fortress capital is consistent but distrusted by the diplomatic corps who until recently were harried by a hostile junta.

Elderly regime henchmen walk the gilded corridors of power with books on parliamentary procedure and schemes to entrench democracy.

Hla Myint Oo, a former diplomat who won a seat in the generals-backed party that dominates the new parliament, found inspiration in Parliament, a book of procedure published in London.

"I read that the British parliament has more than 200 people working in its archives and library," he said. "If I work to set up the same here, I will have left a solid legacy to parliamentary democracy in Burma."

The regime suddenly abandoned Rangoon, the colonial capital, overnight in 2005, telling civil servants to board buses and move with their jobs.

Accommodation was allowed in one zone, government was established in a second zone, a third zone was built for shopping and a fourth zone was filled with hotels.

In one of the world's poorest countries a zoo was built that had an air-conditioned enclosure for penguins.